In U.S. Pat. No. 3,983,017 entitled, "Recovery of Metal Values from Manganese Deep Sea Nodules" by Lester J. Szabo, the teachings of which are incorporated herein by reference, a process is disclosed in which copper, nickel, cobalt and molybdenum are recovered from raw manganese nodules with an aqueous ammoniacal leach solution containing cuprous ions. The process disclosed in U.S. Pat. No. 3,983,017 is a significant breakthrough in the metallurgical art in that it significantly expands the world's source of copper, nickel, cobalt and molybdenum. The process disclosed in U.S. Pat. No. 3,983,017 has come to be called the "cuprion process" and includes the step of contacting ground manganese nodules with an ammoniacal leach solution containing cuprous ions in a reaction vessel to reduce the manganese oxides in the nodules to enable metal values such as copper, nickel, cobalt and molybdenum to be solubilized. The nodule residue is washed with an ammoniacal ammonium carbonate solution to remove these entrained metal values from the residue and place them in a wash-leach solution from which they can be recovered. The reduction liquor can be recycled to the reaction vessel in which the manganese nodules are added. To maintain a sufficient amount of cuprous ions, a reducing gas, such as carbon monoxide, is passed through the reaction vessels. In the cuprion process, metal values are recovered from the wash-leach solution. One advantageous method of recovering the copper and nickel values from the wash-leach solution is to extract them with an oxime type ion exchanger. However, this type of ion exchange reactant is known to be inefficient in extracting cuprous ions and the copper metal values in the wash-leach solution are present predominantly as cuprous ions. In the prior art version of the cuprion process, the wash-leach solution is oxidized with air prior to contacting the oxime extractant to convert the lower valence ions to their more oxidized state. Another reason for oxidizing the wash-leach solution is to liberate carbon monoxide which is complexed with cuprous ion and thereby prevent the slow liberation of carbon monoxide in the subsequent wash operations.
Another similar metal recovery process in which manganese nodules are reduced to enable metal values to be recovered therefrom is the so called fluid bed process. This process is set forth in U.S. patent application Ser. No. 500,493 entitled "Two-Stage Fluid Bed Reduction of Manganese Nodules" by H. E. Barner, D. S. Davies and L. J. Szabo, filed Aug. 26, 1974, the teachings of which are incorporated herein by reference.
In this process, manganese ore nodules are treated in a two-stage fluid bed process to produce a leachable product. In the first stage, dried nodules are calcined using direct fuel injection under a neutral or slightly oxidizing atmosphere to remove about one-half of the oxygen content. Subsequently, in the second stage, the calcined nodules are reduced with synthesis gas to render the metal values leachable. The metal values such as copper and nickel are leached from the cooled nodules with an ammonia-ammonium carbonate leach solution with air as an oxidant. It should be noted that prior to leaching, the ore is reduced to a point where the metal values are present as the metals themselves. In order to get the metals into solution they must be oxidized. A patent illustrating that oxidation during leaching is necessary in processes such as the fluid bed process is U.S. Pat. No. 1,487,145 by M. H. Caron.
In the Caron patent, nickel is recovered from lateritic ores by reducing the nickel in the ore to nickel metal. Thereafter, the nickel metal is oxidized by air in the presence of ammonia. The air causes the nickel to oxidize and dissolve in the ammoniacal solution.
Two other publications which teach to oxidize leach solutions with air to dissolve the metal values are given below:
U.S. Pat. No. 2,556,215 entitled "Method of Producing High-Grade Iron Oxide from Ores Rich in Nickeliferous Pyrrhotite" by Queneau et al, and,
Experiments in Processing Marine Nodules, Brooks, P.T. et al., Processing Congress, Prague, Czech, June, 1970, p. 331.